This invention relates to a gas blast electric circuit breaker and, more particularly, to a circuit breaker of this type which includes main contacts and auxiliary electrodes and incorporates a puffer structure to compress a volume of insulating gas to be blown over the main contacts and auxiliary electrodes and magnetic means for producing self-induced rotation of an arc produced by separation of the contacts around the periphery of the auxiliary electrodes.
In a gas blast circuit breaker using sulfur hexafluoride (SF.sub.6) as the insulating gas, the gas is compressed during breaker opening to provide the gas pressure required for interruption of a high power circuit. This compression requires a relatively massive, high power operating mechanism. Attempts have been made in the prior art to improve the interruption capability of gas blast circuit breakers by driving the arc produced at contact separation in a ring around an auxiliary electrode by a self-induced magnetic field, produced by the arc current flowing through magnetic members located in a ring electrode. This effort has been founded upon the concept that in a plain-break, the arc can reignite in its earlier stationarily heated gas, which has a lower resistance than cold gas. By driving the arc around a ring electrode, the arc is continuously driven into cold gas, while the gas in the path already traveled by the arc can cool off so that at the time when the recovery voltage rises, the arc has to reignite in cooler gas than for a plain-break circuit breaker. A problem for this system is that as the current being interrupted increases, the arc speed around the ring electrode increases, so that for high current the arc moves so fast that it runs into still hot gas produced by the arc in its previous passage around the ring electrode. This fact has been responsible for low voltage ratings at high currents in this type of circuit breaker (e.g., 7.2 kilovolts at 31,000 amps.sub.RMS and 3.6 KV at 40 K amps.sub.RMS).
A prior art example of such a circuit breaker is U.S. Pat. No. 4,032,736, issued June 28, 1977 to Ruffieux et al. Ruffieux et al. describes a fixed chamber breaker in which a pair of arcs 12, 13 is created, one of which is rotated about an annular intermediate electrode 9, and the other arc remains stationary between a centrally-located conductive pin 10 and the interior of contact nozzle pipe 2a, 2b. The rotating arc 12 heats the insulating gas rising its pressure to an adequate level to extinguish the stationary arc.
A magnetic arc rotating means is disclosed in U.S. Pat. No. 4,079,219, issued Mar. 14, 1978 to Weston. Weston describes a system in which a static volume of SF.sub.6 occupies the circuit interrupter, and an arc drawn by opening of the main contacts is transferred to concentric rings 51 and 57, and due to a magnetic field produced by current flowing through windings 50 and 76, respectively, the arc is caused to rotate about the circumference of the rings 51 and 77 through the relatively static gas. Weston describes use of a puffer type arrangement to produce a "relatively small gas blast action which permits the interruption of relatively low currents which might not otherwise be moving rapidly enough within the dielectric gas to be effectively interrupted." (See column 10, lines 9-13). This low current, low voltage puffer in Weston is directed to moving an arc lacking the necessary current to create a magnetic field of adequate strength to rotate the arc, so that the small puffer volume within tube 80 and the restricted flow through slots 100 is sufficient to produce a "small gas blast action".
Another prior art arc interrupter is disclosed by Votta in U.S. Pat. No. 4,052,577, issued Oct. 4, 1977. As shown in FIG. 11, a fixed contact finger cluster 408 and a movable contact 401 carry the operating current. At the opening of the contacts, a coaxial winding 412 connected to movable contact 401 causes rotation of an arc drawn between arcing ring 411 and the contact tips of finger cluster 408, and insulating gas is provided from volume 405 to produce a flow of gas over the contacts. The system is limited to low voltage ratings at high currents, and uses a blast of insulating gas to start the arc movement through a static gas.
Accordingly, it is an object of the instant invention to provide a puffer breaker, which uses a self-induced field to rotate an arc capable of interrupting high voltage, high current circuits.
It is a further object of the instant invention to provide an apparatus and method for rotating an arc between electrodes in a moving stream of insulating gas.